FIELD OF THE INVENTION
This invention relates to implantable defibrillation and pacing leads and more particularly to devices of this type which employ fixation structure operative to engage and draw tissue laterally toward the distal end of the defibrillation or pacing lead.
The instant fixation devices are appropriate for minimally invasive defibrillation and use with new, deployable defibrillation leads which are implanted without the currently practiced thoracotomy procedures. The implantation of these leads requires making a small incision in the chest to gain access to the pericardial space. The defibrillation leads are then threaded through the incision and into the pericardial space either alone or through the lumen of a thin walled guiding catheter. Once initially placed in his fashion, a deployment action is performed to expand the surface area of the lead. At this point, the lead is generally held against the myocardial surface by the pericardium.
Because of the lubricious conditions which exist within that space, and the need to more precisely position the leads for defibrillation, lead fixation is required. Fixation to the pericardial sack is the safest approach since it completely avoids accidental laceration of the myocardial circulation. For additional safety, the instant fixation device utilizes hooks that penetrate through the pericardium and return to the lead. These designs do not leave a sharp, pointed object imbedded in the tissue. Still further, the fixation means needs to be robust in order to remain effective through the violent contractions experienced by the heart during initial defibrillation testing. Also, the ability to control device fixation using only simple axial, back-and-forth, "camera cable release-like" motions on common, off-the-shelf devices such as guidewires and stylets is highly desired. This is due, in part, to the fact that the lead may be partially or completely deployed and that lead body rotation and traction due to the remoteness of the insertion site may not be useful technique at this stage of the implant. It also should be noted that although the instant focus is pericardial fixation, these same fixation concepts can be applied to myocardial tissue if knowledge of the local circulation is accurate.